Abstract: New on-axis, optically addressable spatial light modulators (SLMs) and methods of use are described. The new SLMs include a film of a photochromic material and a non-polarizing beam splitter arranged such that read and write beams counterpropagate with one another, and the read beam is separated from the path of the write beam after being transmitted through the photochromic material film without losing any polarization information encoded on the read beam. The new SLMs are advantageously implemented in incoherent-to-coherent optical converters and all-optical joint transform correlators.